2 Chronicles 6:4
And he said, Blessed be the LORD God of Israel, who hath with his hands fulfilled that which he spake with his mouth to my father David, saying, And he said, Blessed be the LORD God of Israel, who hath with his hands fulfilled that which he spake with his mouth to my father David, saying,
The verse belongs to Solomon's vocal, public prayer at the dedication after the temple was erected, offered in the presence and hearing of the people of Israel in public worship before the congregation. In pronouncing this blessing he stood facing the altar on a brazen scaffold in the court, with hands lifted to heaven before the standing congregation. For the dedicatory prayer he knelt upon the brazen scaffold in the presence and hearing of the people. The words of the prayer were preserved and recorded in the Bible.
In the verse he blesses the Lord God of Israel because God has fulfilled by His hands and actions what He spoke with His mouth and promised to David his father. The completed temple is presented as the fulfillment of God's promise to David. The fulfilled word was that David himself, though he wanted to build a house for God, would not build it, but his son would build it for God's name. The fulfillment included God's choice of Jerusalem as the place for His name.
Solomon saw the fulfillment in his having risen up in David's place on the throne of Israel, with David established as ruler over Israel, and in his having built the house for the name of the Lord. The fulfillment further included putting the ark of the covenant inside the house. After the prayer ended, God answered by sending fire from heaven that consumed the burnt offering. God also answered by appearing to Solomon by night to say that He had heard his prayer.